Field
The present disclosure is related generally to wireless systems, and more specifically, to providing location estimation of user equipment (UEs) in a cellular network.
Related Art
A related art cellular UE such as a smartphone transitions between two modes: CONNECTED when it is fully functional and transmitting and receiving messages and IDLE, when it suspends most of its activities in order to save battery power. In related art implementations, after the UE is done with some communication process, the UE waits for a period of time known as the radio resource control (RRC) Inactivity Timer. If there is no new data transmission or reception during that time, the UE enters the IDLE mode.
During IDLE mode, the UE does not monitor most of the data and control channels and participate in sending control information. A consequence of the IDLE mode is that, if the UE is moving when it is IDLE, the UE may move to the coverage area of a new base station and the network may not be aware of this transition. If a new data comes for the UE while it is IDLE, the Mobility Management Entity (MME) of the core network of the operator has to first send a paging message to the UE asking it to transition to CONNECTED mode so that the UE becomes capable of receiving the data. However, because the UE may have moved from its last known base station just before it went IDLE, the MME may not know the location of the UE. Thus, the MME sends the paging message meant for the UE to a large number of base stations to which the UE has been initially registered, and each of these base stations broadcast the paging message.
FIG. 1 illustrates paging and tracking area update for IDLE UEs. For purposes of paging, base stations (BS) are grouped into what is known as Tracking Areas (TA). In FIG. 1, three TAs (TA 1, TA 2 and TA 3) are shown. The UE is initially registered to a group of TAs which is called a TA List. As shown in FIG. 1, UE A is initially (at time t0) registered to TAs TA 1 and TA 2. Thus the TA List of UE A is {TA 1, TA 2}. Assume that UE goes IDLE at time t0 and is also mobile. At time instant t1, the UE is in a base station belonging to TA 2. If a new data comes for the UE at this time, the MME sends a paging message to all base stations in TA 1 and TA 2, which form the TA list for the UE. The base stations in turn broadcast the paging messages and the UE receives the message.
When the UE is IDLE, there is a possibility that the UE moves to a base station which is not in the TA list. This is shown at time t2, when the UE has reached a base station belonging to TA 3 (Assume that the UE went IDLE at t0 and remained IDLE from t0 to t1 and then t2). The UE does monitor certain system information periodically even in IDLE state and can determine which TA it belongs to. If the UE detects that it is in a new TA that is not in its TA list, the UE initiates a TA Update procedure with the MME.
A large TA list increases the cost of paging (paging can constitute 30-40% of a MME's signaling capacity) while a small TA list could mean more frequent TA updates. The frequent TA updates may drain UE battery power, thereby taking away the advantage of going to an IDLE state. Thus, optimizing paging and TA update procedures are considerations for cellular operators. The solution lies in an intelligent design of TA list by including those base stations where the UE is most likely to be found in the future. The related art looks for efficient means to predict the location of an IDLE UE at a future time.
Related art implementations have looked into paging optimization by trying to predict the location of an IDLE UE. There have been studies on basic mobility pattern (i.e. page the last 5 eNodeBs where the UE was observed). More advanced studies have looked at estimating a UE location based on device-to-device communication information or small cell communications.
An example of a related art implementation for estimating a UE location based on device-to-device communication information can involve using UE discovery for paging optimization. In such implementations, UE devices participate in peer to peer communication networks in which discovery signals are transmitted, and a cellular active UE device in the vicinity of the transmitter eavesdrops on the peer discovery signaling and detects the presence of the cellular inactive UE device. One example of such a related art implementation can be found in US Patent Publication No. 2014/0024378, herein incorporated by reference in its entirety for all purposes.
An example of a related art implementation for estimating a UE location based on small cell communications can involve paging optimization in small cell networks by using gateways. Such a related art implementation can involve receiving a paging message having a permanent user identity of a user for a specific UE, and determining a set of small cells for sending the paging message based on the small cell last visited by the UE as identified by the permanent user identity. One example of such a related art implementation can be found in US Patent Publication No. 2014/0106790, herein incorporated by reference in its entirety for all purposes.